Micro black hole

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A micro black hole, also called a quantum mechanical black hole and inevitably a mini black hole, is simply a tiny black hole for which quantum mechanical effects play an important role.

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[edit] Explanation

The smallest mass it is believed a black hole could have, for the classical black hole description to still make any sense at all, is probably of the order of the Planck mass, which is about 2 × 10−8 kg or 1.1 × 1019 GeV. At this scale the black hole thermodynamic formulae predict the mini-black hole would have an entropy of only 4π nats; a Hawking temperature of TP / 8π, requiring thermal energy quanta comparable in energy to almost the mass of the entire mini black hole; and a Compton wavelength equal to the black hole's Schwarzschild radius (this distance being equal to the Planck length). This is the point where a classical gravitational description of the object stops being retrievable with merely small quantum corrections, but in effect completely breaks down.

The existence of black holes of this mass is purely hypothetical but if primordial black holes exist, they might reach this condition as the final stage of runaway evaporation due to Hawking radiation.

Such an energy is orders of magnitude greater than can be produced on Earth in particle accelerators such as the Large Hadron Collider (maximum about 14 × 103 GeV), or detected in cosmic ray collisions in our atmosphere. It is estimated that to collide two aggregates of fermions to within a distance of a Planck length with the currently achievable magnetic field strength would require a ring accelerator about 1000 light years in diameter to keep the aggregates on track. Even if it were possible, any collision product would be immensely unstable, and almost immediately disintegrate.

Some string theorists have suggested that the multiple dimensions postulated by string theory might make the effective strength of gravity many orders of magnitude stronger at small distances (very high energies). This might effectively lower the Planck energy, and perhaps make black-hole-like descriptions valuable even at slightly lower masses. But this is highly speculative.

Others have wondered about the basic assumptions of the quantum gravity program, and whether there is really a compelling case to believe in Hawking radiation[1]. It is only these quantum assumptions which lead to the crisis at the Planck mass: in classical general relativity, a black hole could in principle be arbitrarily small.

Physicist Brian Greene has suggested that the electron may be a micro black hole; see electron black hole. Small black holes would look like elementary particles because they would be completely defined by their mass, charge and spin. On this view, the significance of the Planck mass is that it marks a transition where the Hawking semi-classical approximation breaks down, and a fully quantum mechanical description of the system becomes required. Gravitationally dominated "black hole"-like structures might still exist with these lower masses, but the emission of Hawking radiation would be suppressed by quantum effects, just as an electron constantly accelerating round an atom does not radiate, despite the apparent predictions of classical electrodynamics.

All that can be said with certainty is that current predictions for the functioning of a black hole with a mass less than Planck mass are inconsistent and incomplete.

[edit] See also

Classification by type:

Classification by mass:

[edit] External links

[edit] References

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